GA contract question

I signed a contract to go under a GA to write for a specific company. Do most companies have a standard contract that GA's use? Or do GA's tend to make up there own. My GA says once an agent signs on with him that the agent can never become a GA with the companies that his brokerage represents unless he releases the agent. In other words, he claims his contract binds an agent to him for life with his companies....This sounds fishy to me any input would be helpful.